Accordion is a handheld musical instrument used mostly in folk music. This portable instrument has rectangular bellows, with keyboards on both sides of them. Instead of piano-styled keys, these keyboards have a series of buttons or levers. The expansion and contraction of these bellows between the hands, and the pressing of these buttons produce the sound. The former action results in the airflow moving across the reeds. The buttons are pressed in a perpendicular direction to the movement of the bellows. Traditionally, the right-hand keyboards produce treble sounds, whereas the left-hand set provides bass sounds. There is a variation in the construction methods, internal materials, tone colors, actions, and tunings of accordions. The keyboard systems used in these products may also vary.

In 1829, Cyrill Demian patented an instrument known as the accordion, in Vienna. This musical instrument bore hardly any resemblance to the present day accordions. This instrument could play two different chords by the depression of only one key. The button accordions and the hand harmonicas soon became popular. Since, then Accordions have developed over the years, and are now available in a variety of styles.

The main types of Accordions available now-a-days include the diatonic button accordions, and the chromatic button accordion. There are also hybrid and other varieties of accordions such as those adopting the Stradella bass system. The folk music of Scotland and the Basque people of Spain are played using uniquely-styled accordions. The main difference between the two is the position and tone of the buttons on these musical instruments.